Snap-action switch with bracket for preloading blade and temperature compensation means



SNAP ACTION SWITCH WITH BRACKET FOR PRELOADING BLADE AND TEMPERATURE COMPENSATION MEANS Filed April 1, 1964 Oct. 11, 1966 R. R. HELLMAN 3,278,700

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JEoZerz R He [imam United States Patent Office 3,278,790 Patented Oct. 11, 1966 The present invention relates to an electrical switch for controlling the flow of electrical energy between two terminals and more particularly to such a switch which 7 is capable of accurately functioning even over an extremely wide range of ambient temperatures.

Switches of the type to which the present invention relates generally have a one-piece spring blade with a contact carrying free end. The blade is of the snap-acting, over center type and has an operating point which if linearly moved beyond a prescribed limit sufficient distorts the blade to efiect the snap-action and a subsequent movement of the free contact end from one position to another. At one position the blade, which carries current, has its contact engaging one terminal to complete a circuit while in the other position the blade contact engages another terminal to complete another circuit. The movement of the blade is maintained within a range by two spaced apart stop members. The amount of movement of the operating point from one stop member until the blade shifts from one contact to the other is precisely determined and required to be maintained throughout the operating temperatures to which the switch may be subjected.

While the above-type switches have been found satisfactory in environmental condition having a normal range of ambient temperatures when the ambient temperature range is increased, as for example from minus 300 degrees to plus 1000 degrees F., these switches have not been able to precisely maintain the movement required to cause actuation. Generally, the difficulties have been traceable to a distortion or change of dimensional relationship of the various parts of the switch to each other. In addition to loss of preciseness in operation generally the materials heretofore used to form the parts of the switch have not been capable of retaining their normal physical properties at the higher temperatures with a consequent loss of ability to operate durably without malfunctioning.

It is accordingly an object of the present invention to provide an electrical switch which is capable of functioning over an extremely wide environmental temperature range but yet maintain its preciseness of operability throughout the range.

Another object of the present invention is to provide a switch which is constructed of materials capable of substantially retaining their physical properties over wide temperature conditions and which minimizes distortion or changes in the dimensional relationship between the various parts at different temperatures.

A further object of the present invention is to provide a linearly actuated electric switch which is durable in use at any temperature in a wide ambient temperature range, is composed of few parts and is relatively inexpensive to manufacture.

In carrying out the present invention the specific embodiment of the electrical switch hereinafter disclosed includes a base having posts secured thereon with the post and the base being formed of different materials but yet having a somewhat similar temperature coefficient of expansion. There are three posts with each of the posts carrying a contact, one of the contacts consisting of a spring blade that is formed to have compression and tension members intermediate its ends with one end being secured to its post and the other ends being free and carrying a contact. The other two posts each carry a contact supporting member in position to be engaged by the contact carried by the blade. The blade is caused to move between the two contacts by a linear movement on a point of the tension member and the extent of movement of the blade is controlled by a stop mounted on the base and a stop carried by the post that carries the blade. The movement of the point from its normal position where it engages a stop to the position where the blade is actuated to shift its engagement from one contact to the other is a distance which is required to be accurately maintained irrespective of the operating environment of the switch.

Electrical connections are made to the contacts by lead wires that extend through apertures formed in the base and extend into holes formed in the posts where they are brazed or otherwise secured by a hardened fused material thereto, thus eliminating the base as the supporter of the lead wire. By the above structure it has been found that such a switch is capable of functioning over a wide range of temperatures and at each temperature in the range is capable of being operated to shift from one contact to another by substantially the same movement of the operating point from its stop position.

Other features and advantages will hereinafter appear.

In the drawing:

FIGURE 1 is an elevation of the switch of the present invention.

FIG. 2 is a plan thereof.

FIG. 3 is a detail taken on the line 3-3 of FIG. 1, somewhat enlarged.

Referring to the drawing, the switch is generally indicated by the reference numeral 10 and includes a base 11 that in the specific embodiment shown is a rectangular parallelepiped though other shaped bases may be employed if desired. Formed in the base are three spaced apart holes 12, 13 and 14 through which lead wires 15, 16 and 17 extend. The base 11 is formed to have an upper face 18 which is substantially planar and mounted on the face 18 in a manner which will be hereinafter set forth are a plurality of posts 19, 20 and 21 and a stop member 22. The post 19 has secured thereto one end 23 of an elongate, spring blade 24 with the blades other end being free and carrying a contact 25.

The post 19 additionally carries a stop member 26 having a tang 27 formed therein that is positioned to engage the blade 24 to limit upper movement thereof. While the blade 24 and stop member 26 may be secured to the post 19 in any desired manner, in the present embodiment of the invention herein disclosed, the post is formed with an aperture 28 into which the shank of a rivet 29 extends, the rivet being headed over as at 30 to secure the post plade end 23 and stop member together in the relationship shown.

The post 20 carries a terminal bar 31 having a contact 32 with the terminal bar being secured to the post as by a rivet 33 in a manner similar to the post 19 and rivet 30. The post 21 also carries a terminal bar 34 on which is mounted a terminal 35 with a rivet 36 securing the terminal bar 34 to the post 21. It will be appreciated that the terminal bars 31 and 34 extend toward each other with the contact 32 overlying the contact 35 and both contacts 32 and 35 being in the path of travel of the contact 25.

The switch blade 24 is formed as shown in FIG. 2 with a pair of elongate intermediate apertures 37 and 38 which define therebetween a tension portion 39. The outer edge portions 40 constitute compression portions and are suitably deformed to cause tension and compression in the portions. The blade normally assumes the shape shown in FIG. 1 wherein the tension portion is upwardly humped and the compression portions are downwardly humped to cause the contact 25 to be urged clockwise into engagement with the terminal 32. The tang 27 engages the hump of the tension member to limit the height of the hump to assure contact pressure between the contact 25 and terminal 32 and to set the movement from this stop position required to cause actuation.

In order to cause the blade to move counterclockwise and into engagement with the terminal 35, there is an operating area on the tension member denoted by the enclosed dotted area 41 which, if the tension member is en gaged by an actuator 42 shown in dotted lines within this area and moved linearly downward, it changes the dis-- tortion of the tension and compression members to cause the free end of the blade to move counterclockwise with a snap action and thus change engagement between contact 25 and terminal 32 to engagement between contact 25 and terminal 35. In this latter condition, the tension member becomes downwardly humped which is its abnormal condition and only remains so as long as the acactuator forces the operating point below its actuation distance. The stop member 22 limits the movement to which the actuator may force the tension member.

The two terminals 32 and 35 are located a suflicient distance apart to prevent engagement simultaneously by the contact 25 and to prevent arcing between the contact 25 and the terminal not engaged at the voltage values which the switch encounters.

In the operation of the switch, it is desired that a de termined movement of the actuator 42 move the operating point of the blade downward from its stop position against the tang 27 a distance which causes actuation of the switch. Such distance is required to be precisely controlled within for example tolerances of a few tens of thousandths of an inch. Moreover such a distance should remain substantially constant at any temperature within the ambient temperature range at which the switch is to operate. Such requirements may arise for example when a bellows is connected to the actuator 42 and the switch is to be actuated at a particular linear length of the bellows as determined by the pressure therein. As the actuator 42 moves downwardly a precise distance when the switch blade is in the solid line position shown, it causes the switch blade to snap to the dotted position shown to contact the terminal 35. So long as the actuator maintains at least this distance, the blade remains in the dotted line position but as the actuator retreats past its operating distance the blade returns to its solid line position. The distance which the actuator retreats before the blade changes positions is also desired to be maintained substantially constant.

Conduction from the lead Wire through the blade 24, contact 32 and lead wire 16 constitutes a normally closed circuit while a circuit including lead wire 15, blade 24, contact and lead Wire 17 constitutes a normally opened circuit, the switch functioning between these two circuits.

In carrying out the present invention in order to achieve the maintenance of preciseness throughout an extremely wide temperature range the base 11 is formed of a ceramic material, alumina, 94% minimum, having been found particularly satisfactory. Moreover, the posts 19, 2t and 21 together with the lead wires 15, 16 and 1'7 are formed of a metallic material which has a temperature coefiicient of expansion somewhat similar to the temperature coefficients of expansion of the material of the base 11. Thus if the former is formed of alumina, the latter is preferably nickel.

In the embodiment of the invention disclosed, each of the posts 19, 20 and 21 are secured to the base in the same manner as are the lead Wires 15, 16 and 17 secured to their respective posts. Thus referring to FIG. 3, which refers specifically to post 21 and lead wire 17, the other post and lead wire structures being the same, the face 18 of the base has a flat area to which a surface coating 43 of a metallic material such as molybdenum manganese alloy is bonded and then nickel plated. The post has flat bottom and is secured to the base by hardened fused metal indicated by the reference character 44 in FIG. 3 that interconnects the post and the coating. The metal 4 4 may be applied by brazing for example and one material which has been found particularly satisfactory is an gold brazing alloy. The lead wire 17 is secured to post 21 by extending into an aperture 45 formed in the post 21 and a hardened fused metal, indicated by the reference character 46 interconnects the lead wire and the post. The metal 46 may be the 80% gold brazing alloy applied by brazing. Preferably the entrance of the hole 14 at the face 18 is chamfered somewhat to accommodate the flaring caused by the metal 46 to enable the base of the post to be flat against the face 18.

The lead wire 17 has a cross-section that is smaller than the cross-section of the aperture 14- and thus is free therefrom. However, at times the chamfered entrance of the aperture and the metal 46 may become interconnected if the brazing operation that applies metal 44 also inadvertently affects the metal 46. Each of the posts is secured in the manner just described, with the lead wire being free from the apertures 12, 13 and 14 and being held by hardened fused metal to their respective post while each post is held by hardened fused metal to a metallic coated fiat area formed on the face 16 of the base 11.

The material from which the blade may be formed is preferably one of the high temperature super alloys, such as Inconel, Elgiloy or Ren 62 that has been tempered in order that it retains substantially the same physical properties throughout a wide ambient temperature range. In addition, the contact 25 may be formed of silver or other contact materials though a platinium iridium (10%) alloy has been found particularly satisfactory. Moreover, terminals 32 and 35 may also have an insert of this contact material or may be simply flat areas on the support members 31 and 3 s as shown.

The stop member 26 may be formed from stainless steel while the stop member 22 is preferably formed of ceramic as an integral part of the base 11 to have the shape shown. Extending transversely through the base 11 are a pair of mounting holes 47 by which the present invention may be secured to a supporting structure if desired.

It will accordingly be appreciated that there has been disclosed an electric switch which is capable of functioning over a wide temperature range and yet which maintains its preciseness of operation at temperatures within this range. This is achieved by forming the base of the switch from a ceramic material and securing on a face thereof three posts formed of metallic material which have a temperature coefficient of expansion substantially similar to that of the ceramic base. Moreover, in accordance with the present invention, lead wires are employed which are formed of the same material as the posts and the wires are each caused to extend through an aperture formed in the base to be secured to the post and yet be substantially free from the base.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

I claim:

1. An electrical switch for use over a wide range of ambient temperatures of over 500 degrees F. comprising a one-piece body formed of ceramic material to have at least one face with holes extending through said body and open at the face, a plurality of metal posts with each post having a lead wire extending therefrom, means securing each post only on said face to have its lead wire axially aligned with and extend through a hole with there being one post aligned with one hole, said securing means including a metallic coating formed on said face adjacent said hole and a hardened metallic material fused to said post and coating, a first contact means supported on one post, a second contact means supported on another post, a spring contact blade supported on a third post and having a contact normally electrically engaging the first contact means and be actuated by a predetermined movement to be disengaged from the first contact means and engage the second contact means, each of said lead Wires being smaller than its associated hole to thereby be free of the ceramic material for substantially the length of said hole and in which the metallic material of which the posts are formed has a temperature coeflicient of expansion similar to the temperature coefficient of expansion of the material of the body.

2. The invention as defined in claim 1 in which the posts are formed of nickel and the ceramic material is alumina.

3. The invention as defined in claim 1 in which there are two stop means engaging said blade adjacent the third post to limit movement thereof, one of said st-opmeans being supported by said third post and the other being integral with the body and extending from said face toward said blade.

4. An electric switch comprising a body having a face, a post upstanding from said face, an elongate spring contact blade having one end portion secured on said post and having a contact carried by the other end portion, said blade having an intermediate portion formed to provide tension and compression members with actuation of one of said members at an actuation area resiliently deforming the blade to cause the contact to move from its normal position to another position, contact means positioned to engage said contact at its normal position and at its another position, means engaging the one member to be actuated to partially deform said one member in the same direction as the deformation required to cause movement from its normal to its another position adjacent the actuation area and in which the blade has two outer tension member and a compression member, said compression member bowing upwardly to form a bump and the said engaging means engages the hump to decrease the free height of the hump.

5. An electric switch comprising a body having a face, a post upstanding from said face, an elongate spring contact blade having one end portion secured on said post and having a contact carried by the other end portion,

said blade having an intermediate portion formed to provide tension and compression members with actuation of one of said members at an actuation area of said member resiliently deforming the blade to cause the contact to move from its normal position to another position, contact means positioned to engage said contact at its normal position and at its another position, means engaging the one member to be actuated to partially deform said one member in the same direction as the deformation required to cause movement from its normal to its another position, said means partially deforming said member engaging said member between the actuation area of the member and the contact and in which the blade has two outer tension members and a compression member, said compression member bowing upwardly to form a bump and the said engaging means engages the hump to decrease the free height of the hump.

6. The invention as defined in claim 5 in which the means for partially deforming the member includes a flat plate mounted on said post and extending over said blade, said plate having an opening therein aligned with the actuation area and an integral tab depending downwardly therefrom to engage the member.

References Cited by the Examiner UNITED STATES PATENTS 908,679 5/ 1909 Kelley 200122.3 1,111,789 9/ 1914 Freas 200122.3 2,033,410 3/1936 Dezotell. 2,163,409 6/ 1939 Pulfrich 189--36.5 2,549,740 4/1951 Yonkers. 2,574,925 -11/ 1951 Lehane et a1. 2,700,079 1/ 1955 Haydon. 2,707,216 4/1955 Farison. 2,773,955 12/1956 Haydon 200-168 2,776,347 1/ 1957 Allen. 2,840,656 6/ 1958 Roeser. 3,001,269 9/ 1961 Moore et a1 174-152.4 3,117,205 1/ 1964 Adams.

ROBERT K. SCHAEFER, Primary Examiner.

KATHLEEN H. CLAFFY, Examiner.

D. SMITH, JR., Assistant Examiner, 

1. AN ELECTRICAL SWITCH FOR USE OVER A WIDE RANGE OF AMBIENT TEMPERATURES OF OVER 500 DEGREES F. COMPRISING A ONE-PIECE BODY FORMED OF CERAMIC MATERIAL TO HAVE AT LEAST ONE FACE WITH HOLES EXTENDING THROUGH SAID BODY AND OPEN AT THE FACE, A PLURALITY OF METAL POSTS WITH EACH POST HAVING A LEAD WIRE EXTENDING THREFROM, MEANS SE CURING EACH POST ONLY ON SAID FACE TO HAVE ITS LEAD WIRE AXIALLY ALIGNED WITH AND EXTEND THROUGH A HOLE WITH THERE BEING ONE POST ALIGNED WITH ONE HOLE, SAID SECURING MEANS INCLUDING A METALLIC COATING FORMED ON SAID FACE ADJACENT SAID HOLE AND A HARDENED METALLIC MATERIAL FUSED TO SAID POST AND COATING, A FIRST CONTACT MEANS SUPPORTED ON ONE POST, A SECOND CONTACT MEANS SUPPORTED ON ANOTHER POST, A SPRING CONTACT BLADE SUPPORTED ON A THIRD POST AND HAVING A CONTACT BLADE SUPPORTED ON A THIRD POST FIRST CONTACT MEANS AND BE ACTUATED BY A PREDETERMINED MOVEMENT TO BE DISENGAGED FROM THE FIRST CONTACT MEANS AND ENGAGE THE SECOND CONTACT MEANS, EACH OF SAID LEAD WIRES BEING SMALLER THAN ITS ASSOCIATED HOLE TO THEREBY BE FREE OF THE CERAMIC MATERIAL FOR SUBSTANTIALLY THE LENGTH OF SAID HOLE AND IN WHICH THE METALLIC MATERIAL OF WHICH THE POSTS ARE FORMED HAS A TEMPERATURE COEFFICIENT OF EXPANSION SIMILAR TO THE TEMPERATURE COEFFICIENT OF EXPANSION OF THE MATERIAL OF THE BODY. 